Physical and Chemical Changes in Chemistry
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Chemical reactions
Science
Atoms and the periodic table
Understand the difference between physical and
chemical changes and write word and symbol
equations.
An
element
is a substance made from one type of atom.
A
chemical symbol
is a one or two letter representation
for an element.
A substance’s
state
is whether it is a solid, liquid or gas.
Chemical reactions
Physical and chemical changes
Equations
Displacement reactions
Decomposition reactions
Chemical change
A reaction that make new substances.
Physical and chemical changes
Physical change
Matter changes form or state.
Can you think of any others?
melting ice cream
breaking glass
iron rusting
food cooking
6 signs of a
chemical reaction:
1)
fizzing (gas is produced)
2)
colour change
3)
temperature change
4)
light produced
5)
sound produced
6)
smell produced
Physical and chemical changes
It is usually difficult to turn your
products back into reactants.
Physical and chemical changes
Which
is the odd one out?
milkshake mixing firework exploding
water boiling
physical change chemical change physical change
Why
are these examples of chemical reactions?
Physical and chemical changes
●
new product formed
●
light produced
●
gas produced (bubbles)
●
new product formed
●
gas produced (bubbles)
●
colour change
How
can you tell these are examples of chemical reactions?
Physical and chemical changes
●
colour change
●
light produced (flame)
In
which two
test tubes has a chemical reaction
taken place?
A B C
The product is the same as what you start with and
you can easily obtain the butter, flour and sugar
again.
Baking a cake is a chemical reaction.
The product is different from what you start with and
it is difficult to reverse the reaction.
crushing a bag of crisps
Which
of the following is a chemical change?
sherbet fizzing on your tongue
filtering sand and water
mixing watercolour paints
Which
of the following is a physical change?
lighting a birthday candle
cooking a sausage
Physical and chemical changes
1
There are multiple stages
to making cookies.
For each stage, identify
whether it is a physical or
chemical change taking
place and explain how you
know.
Stage 1:
Mixing the chocolate chips into
the dough.
Chemical or physical?
Explanation
Stage 2:
Separating dough into balls.
Chemical or physical?
Explanation
Stage 3:
Baking cookies in the oven.
Chemical or physical?
Explanation
Answers
1
Stage 1:
Mixing the chocolate chips into the dough.
Chemical or physical?
Explanation
physical
●
Chips would be easy to separate again.
●
No new products (still dough and chocolate
chips).
●
No fizzing, colour change, temperature
change, sound or smell.
Answers
1
Stage 2:
Separating dough into balls.
Chemical or physical?
Explanation
physical
●
No new products - still cookie dough, just in
smaller pieces.
●
It would be easy to return back to what you
started with.
●
No fizzing, colour change, temperature
change, sound or smell.
Answers
1
Stage 3:
Baking cookies in the oven.
Chemical or physical?
Explanation
chemical
●
New product formed - baked cookies.
●
Would be difficult to return back to what
you started with.
●
Colour change, smell produced, and bubbling.
Chemical reactions
Physical and chemical changes
Equations
Displacement reactions
Decomposition reactions
Equations
In a chemical reaction substances (
reactants
) react
to make new substances (
products
).
There are chemical reactions happening around us
everyday.
reactants
product
ᐩ
ᐩ
ᐩ
→
Equations are a written representation of the process
that occurs during a chemical reaction.
Equations
reactant
product
reactant
There are
word
equations using the substance names,
iron
+
sulfur
→
iron sulfide
and
symbol
equations using the chemical symbols.
Fe
+
S
→
FeS
ᐩ
→
How to write word equations:
1)
Identify which substances are being
used
- these are your
reactants
.
2)
Identify which substances are being
made
- these are your
products
.
3)
Put reactants’ names on the left and product names on the right.
Equations
For example
Magnesium reacts with oxygen to form magnesium oxide.
magnesium
magnesium oxide
oxygen
ᐩ
→
Fill
in the blank in
the word equation.
Hydrogen reacts with oxygen to form water.
hydrogen
_
_
_
_
_
_
_
_
oxygen
water
ᐩ
→
Fill
in the blank in
the word equation.
Carbon, hydrogen and oxygen react to make ethanol.
hydrogen
_
_
_
_
_
_
_
_
oxygen
ethanol
carbon
ᐩ
ᐩ
→
Fill
in the blank in
the word equation.
Aluminium oxide breaks down into aluminium and oxygen.
aluminium oxide
_
_
_
_
_
_
_
_
oxygen
aluminium
→
ᐩ
Symbol equations
Instead of the names, we use chemical formulae.
Equations
2
H
2
O
2
2
H
2
O
Coefficients
tell you the number of molecules.
Subscript numbers
tell you the molecule’s chemical formula.
H
H
H
H
O
O
O
H
H
O
H
H
ᐩ
→
nitrogen (N
2
)
fluorine (F
2
)
oxygen (O
2
)
Diatomic molecules
Equations
hydrogen (H
2
)
chlorine (Cl
2
)
bromine (Br
2
)
iodine (I
2
)
Some elements hang
around in pairs, rather
than as single atoms.
Watch out for these
when balancing
equations!
Symbol equations
They need to be
balanced
. They must have the same number
of atoms of each element on both sides of the equation.
Equations
Ca
S
Ca
S
How many atoms of calcium are there? How many sulfur atoms?
There is 1 calcium atom and 1 sulfur atom on both sides.
This equation is balanced!
ᐩ
→
Hydrogen reacts with chlorine to make hydrogen chloride.
H
Cl
H
Cl
How many molecules of HCl can I make?
Cl
H
2
2
ᐩ
→
Equations
Hydrogen and chlorine are
diatomic molecules
(their
atoms are found in pairs).
Hydrochloric acid reacts with zinc to produce zinc
chloride and hydrogen.
Zn
H
Cl
How many molecules of HCl do I need?
Cl
H
2
H
Zn
Cl
2
ᐩ
→
ᐩ
Equations
Hydrogen reacts with oxygen to
produce water.
Balance
the equation.
2
2
O
2
H
2
O
H
2
Lithium reacts with chlorine to
produce lithium chloride.
Balance
the equation.
2
2
Cl
2
LiCl
Li
ᐩ
→
ᐩ
→
Magnesium reacts with oxygen to produce
magnesium oxide.
How many
molecules of magnesium oxide will I make?
2
2
O
2
MgO
2 Mg
ᐩ
→
Hydrogen reacts with nitrogen to produce ammonia.
How many
molecules of hydrogen do I need?
3
3
N
2
2 NH
3
H
2
ᐩ
→
2
a)
Write
the word equation and
add
the symbols to the symbol equations.
Equations
2
a)
Write
the word equation and
add
the symbols to the symbol equations.
Answers
potassium + oxygen
→
sodium + fluorine
→
carbon + oxygen
→
calcium + chlorine
→
K
F
CO
2
Ca
potassium
oxide
sodium
fluoride
carbon
dioxide
calcium
chloride
2
b)
Write
the word equation and
balance
the symbol equations.
Equations
2
b)
Write
the word equation and
balance
the symbol equations.
Answers
beryllium + oxygen
→
hydrogen + bromine
→
iron + oxygen
→ iron oxide
gallium + sulfur
→
2
2
4
2 3
beryllium
oxide
hydrogen
bromide
gallium
sulfide
Chemical reactions
Physical and chemical changes
Equations
Displacement reactions
Decomposition reactions
Displacement
Displacement reactions
When one element takes the place of another in a
compound.
All displacement reactions follow the same format:
A +
B
C
→ A
C
+
B
C
B
B
C
A
A
+
→
+
Displacement reactions
Example
If magnesium is added to copper sulfate, magnesium and
copper swap places to make magnesium sulfate and copper.
Mg
CuSO
4
MgSO
4
Cu
When magnesium is added to
copper sulfate, magnesium
displaces copper to make
magnesium sulfate and copper.
Write
the word equation for this
reaction.
When zinc is added to lead
sulfate, zinc displaces lead to
make zinc sulfate and lead.
Write
the word equation for this
reaction.
zinc +
lead
sulfate
→
zinc
sulfate
+ lead
When magnesium (Mg) is added
to copper sulfate (CuSO
4
),
magnesium displaces copper to
make magnesium sulfate
(MgSO
4
) and copper (Cu).
Write
the symbol equation for
this reaction.
When zinc (Zn) is added to lead
sulfate (PbSO
4
), zinc displaces
lead to make zinc sulfate
(ZnSO
4
) and lead (Pb).
Mg +
CuSO
4
→ MgSO
4
+ Cu
Write
the symbol equation for
this reaction.
Zn +
PbSO
4
→ ZnSO
4
+ Pb
NaCl + Ag
NaAg + Cl
If sodium (Na) is added to silver chloride (AgCl), a
displacement reaction occurs.
What
are the reactants?
AgCl + Na
NaCl + Ag
NaAg + Cl
If sodium (Na) is added to silver chloride (AgCl), a
displacement reaction occurs.
What
are the products?
AgCl + Na
How
can you tell if an equation is displacement?
The two reactants are added together to form one
product.
There are always two reactants and two products.
Two elements in the reactants will have swapped
places in the products.
Displacement reactions
a)
Complete
the word equations for these displacement
reactions.
i)
calcium
___________
+ lithium → lithium chloride +
calcium
ii)
sodium chloride + fluorine → sodium fluoride +
_________
iii)
iron oxide + aluminium → aluminium
_________
+ iron
iii)
silver
________
+ copper → copper nitrate + silver
3
Answers
a)
Complete
the word equations for these displacement
reactions.
i)
calcium
___________
+ lithium → lithium chloride +
calcium
ii)
sodium chloride + fluorine → sodium fluoride +
_________
iii)
iron oxide + aluminium → aluminium
_________
+ iron
iii)
silver
________
+ copper → copper nitrate + silver
3
chloride
chlorine
oxide
nitrate
Displacement reactions
b)
When zinc Zn is added to copper nitrate Cu(NO
3
)
2
, zinc
displaces lead to make zinc nitrate Zn(NO
3
)
2
and copper Cu.
3
i)
Write
the word equation for this reaction.
ii)
Complete
the symbol equation for this
reaction.
Zn +
Cu(NO
3
)
2
→
Answers
b)
When zinc Zn is added to Copper nitrate Cu(NO
3
)
2
,
zinc displaces lead to make zinc nitrate Zn(NO
3
)
2
and copper
Cu.
3
i)
Write
the word equation for this reaction.
ii)
Complete
the symbol equation for this
reaction.
Zn +
Cu(NO
3
)
2
→
zinc + copper nitrate → zinc nitrate + copper
Zn(NO
3
)
2
+ Cu
Chemical reactions
Physical and chemical changes
Equations
Displacement reactions
Decomposition reactions
Decomposition reactions
Decomposition reactions
When a substance breaks down into two or more smaller
components.
All decomposition reactions follow the same format:
A
B
→
A
+
B
B
B
A
A
+
→
Decomposition reaction example
When heated, sodium hydrogen carbonate
breaks down into sodium carbonate, water
and carbon dioxide.
Decomposition reactions
If sodium hydrogen carbonate is added to
a cake mixture, the cake rises when it
bakes. Why do you think this is?
Decomposition reaction example
When heated, copper carbonate breaks down into copper
oxide and carbon dioxide.
Decomposition reactions
CuCO
3
CuO
CO
2
→
When heated, copper carbonate (CuCO
3
) breaks
down into copper oxide (CuO) and carbon dioxide
(CO
2
).
Write
the word equation for this reaction.
Complete
the symbol equation for this reaction.
CuCO
3
→
copper carbonate → copper oxide + carbon dioxide
CuO + CO
2
O
2
CO
2
When heated, magnesium carbonate breaks down
into magnesium oxide and
which
other product?
H
2
2
3
How many
reactants are there in decomposition?
1
Decomposition reactions
a)
Complete
the word equations for these decomposition reactions.
i)
beryllium carbonate →
__________
oxide + carbon
dioxide
ii)
calcium carbonate → calcium oxide +
________
________
iii)
iron oxide →
__________
+ oxygen
b)
Complete
the symbol equations for these decomposition
reactions.
i)
ZnCl
2
→ Zn +
______
ii)
2 Fe
2
O
3
→ 4
_______
+ 3 O
2
4
Answers
a)
Complete
the word equations for these decomposition reactions.
i)
beryllium carbonate →
__________
oxide + carbon
dioxide
ii)
calcium carbonate → calcium oxide +
_______ _______
iii)
iron oxide →
__________
+ oxygen
b)
Complete
the symbol equations for these decomposition
reactions.
i)
ZnCl
2
→ Zn +
______
ii)
2 Fe
2
O
3
→ 4
_______
+ 3 O
2
4
beryllium
carbon dioxide
iron
Cl
2
Fe
Decomposition reactions
c)
Identify
if the following word equations represent displacement
reactions or decomposition reactions.
4
Answers
c)
Identify
if the following word equations represent displacement
reactions or decomposition reactions.
4
✔
✔
✔
✔
Decomposition reactions
d)
Identify
if the following symbol equations represent
displacement reactions or decomposition reactions.
4
Answers
d)
Identify
if the following symbol equations represent
displacement reactions or decomposition reactions.
4
✔
✔
✔
✔
Chemical reactions
●
Changes to substances can be
physical
or
chemical.
●
When matter changes but is still the same substance, this is a
physical
change.
●
Chemical
reactions create new products.
●
Chemical
equations
can be written as word or symbols.
●
Symbol equations have to balance (same number of atoms of each
element on both sides).
●
When a substance breaks down into two or more smaller substances,
this is
decomposition.
●
Displacement
reactions occur when an element takes the place of
another in a compound.
Learn about physical and chemical changes in chemistry, including the differences between them, word and symbol equations, the periodic table of elements, and identifying chemical reactions through various signs and examples.
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Presentation Transcript
Chemical reactions Understand the difference between physical and chemical changes and write word and symbol equations. Science Atoms and the periodic table
Keywords An element is a substance made from one type of atom. A chemical symbol is a one or two letter representation for an element. A substance s state is whether it is a solid, liquid or gas.
Lesson outline Chemical reactions Physical and chemical changes Equations Displacement reactions Decomposition reactions
Physical and chemical changes E Physical change Matter changes form or state. Chemical change A reaction that make new substances. melting ice cream breaking glass iron rusting food cooking Can you think of any others?
Physical and chemical changes E 6 signs of a chemical reaction: 1) fizzing (gas is produced) 2) colour change 3) temperature change 4) light produced 5) sound produced 6) smell produced It is usually difficult to turn your products back into reactants.
Physical and chemical changes C Which is the odd one out? milkshake mixing firework exploding water boiling physical change chemical change physical change
Physical and chemical changes E Why are these examples of chemical reactions? new product formed light produced gas produced (bubbles) new product formed gas produced (bubbles) colour change
Physical and chemical changes E How can you tell these are examples of chemical reactions? colour change light produced (flame)
C In which two test tubes has a chemical reaction taken place? A A B C B C
C True or false? Baking a cake is a chemical reaction. False True F T Justify your answer The product is the same as what you start with and you can easily obtain the butter, flour and sugar again. The product is different from what you start with and it is difficult to reverse the reaction. A B
C Which of the following is a chemical change? crushing a bag of crisps A sherbet fizzing on your tongue B filtering sand and water C
C Which of the following is a physical change? mixing watercolour paints A lighting a birthday candle B cooking a sausage C
Task 1 Physical and chemical changes P Stage 1: Mixing the chocolate chips into the dough. There are multiple stages to making cookies. Chemical or physical? Explanation For each stage, identify whether it is a physical or chemical change taking place and explain how you know. Stage 2: Separating dough into balls. Chemical or physical? Explanation Stage 3: Baking cookies in the oven. Chemical or physical? Explanation
Task 1 Answers P Stage 1: Mixing the chocolate chips into the dough. Chemical or physical? physical Explanation Chips would be easy to separate again. No new products (still dough and chocolate chips). No fizzing, colour change, temperature change, sound or smell.
Task 1 Answers P Stage 2: Separating dough into balls. Chemical or physical? physical Explanation No new products - still cookie dough, just in smaller pieces. It would be easy to return back to what you started with. No fizzing, colour change, temperature change, sound or smell.
Task 1 Answers P Stage 3: Baking cookies in the oven. Chemical or physical? chemical Explanation New product formed - baked cookies. Would be difficult to return back to what you started with. Colour change, smell produced, and bubbling.
Lesson outline Chemical reactions Physical and chemical changes Equations Displacement reactions Decomposition reactions
Equations E In a chemical reaction substances (reactants) react to make new substances (products). There are chemical reactions happening around us everyday. product reactants
Equations E Equations are a written representation of the process that occurs during a chemical reaction. reactant reactant product There are word equations using the substance names, iron + sulfur iron sulfide and symbol equations using the chemical symbols. Fe + S FeS
Equations E How to write word equations: 1) Identify which substances are being used - these are your reactants. 2) Identify which substances are being made - these are your products. 3) Put reactants names on the left and product names on the right. For example Magnesium reacts with oxygen to form magnesium oxide. magnesium oxygen magnesium oxide
C Fill in the blank in the word equation. Hydrogen reacts with oxygen to form water. ________ water hydrogen oxygen
C Fill in the blank in the word equation. Carbon, hydrogen and oxygen react to make ethanol. ________ ethanol carbon hydrogen oxygen
C Fill in the blank in the word equation. Aluminium oxide breaks down into aluminium and oxygen. ________ aluminium aluminium oxide oxygen
Equations E Symbol equations Instead of the names, we use chemical formulae. 2 H2 O2 2 H2O H O O O H Coefficients tell you the number of molecules. Subscript numbers tell you the molecule s chemical formula.
Equations E Diatomic molecules hydrogen (H2) H Some elements hang around in pairs, rather than as single atoms. oxygen (O2) O nitrogen (N2) N fluorine (F2) F chlorine (Cl2) Cl Watch out for these when balancing equations! bromine (Br2) Br I iodine (I2)
Equations E Symbol equations They need to be balanced. They must have the same number of atoms of each element on both sides of the equation. S S How many atoms of calcium are there? How many sulfur atoms? There is 1 calcium atom and 1 sulfur atom on both sides. This equation is balanced!
Equations E Hydrogen and chlorine are diatomic molecules (their atoms are found in pairs). Hydrogen reacts with chlorine to make hydrogen chloride. 2 Cl Cl Cl 2 How many molecules of HCl can I make?
Equations E Hydrochloric acid reacts with zinc to produce zinc chloride and hydrogen. Cl Zn 2 Cl Zn Cl 2 How many molecules of HCl do I need?
I do We do E C Balance the equation. Balance the equation. Hydrogen reacts with oxygen to produce water. Lithium reacts with chlorine to produce lithium chloride. 2 H2 O2 2 H2O Li Cl2 LiCl 2 2
C Magnesium reacts with oxygen to produce magnesium oxide. 2 Mg O2 MgO 2 How many molecules of magnesium oxide will I make?2
C Hydrogen reacts with nitrogen to produce ammonia. 3 H2 N2 2 NH3 How many molecules of hydrogen do I need?3
Task2 Equations P a) Write the word equation and add the symbols to the symbol equations. Reaction Word equation Symbol equation 4 __ + O2 2 K2O Na + __ NaF Potassium reacts with oxygen to make potassium oxide. Sodium reacts with fluorine to make sodium fluoride. C + O2 ___ Carbon reacts with oxygen to produce carbon dioxide. __ + Cl2 CaCl2 Calcium reacts with chlorine to make calcium chloride.
Task2 Answers P a) Write the word equation and add the symbols to the symbol equations. Reaction Word equation Symbol equation potassium oxide potassium + oxygen 4 __ + O2 2 K2O Na + __ NaF F Potassium reacts with oxygen to make potassium oxide. K sodium fluoride sodium + fluorine Sodium reacts with fluorine to make sodium fluoride. carbon dioxide CO2 C + O2 ___ carbon + oxygen Carbon reacts with oxygen to produce carbon dioxide. calcium chloride Ca __ + Cl2 CaCl2 Calcium reacts with chlorine to make calcium chloride. calcium + chlorine
Task2 Equations P b) Write the word equation and balance the symbol equations. Reaction Word equation Symbol equation Beryllium reacts with oxygen to produce beryllium oxide. _ Be + O2 2 BeO Hydrogen and bromine produce hydrogen bromide. Br2+ H2 _HBr Iron reacts with oxygen to make iron oxide. _ Fe + 3 O2 2 Fe2O3 Gallium reacts with sulfur to produce gallium sulfide. _Ga + _S Ga2S3
Task2 Answers P b) Write the word equation and balance the symbol equations. Reaction Word equation Symbol equation beryllium oxide Beryllium reacts with oxygen to produce beryllium oxide. beryllium + oxygen _ Be + O2 2 BeO 2 hydrogen bromide Hydrogen and bromine produce hydrogen bromide. hydrogen + bromine Br2+ H2 _HBr 2 Iron reacts with oxygen to make iron oxide. iron + oxygen iron oxide _ Fe + 3 O2 2 Fe2O3 2 3 4 gallium sulfide gallium + sulfur Gallium reacts with sulfur to produce gallium sulfide. _Ga + _S Ga2S3
Lesson outline Chemical reactions Physical and chemical changes Equations Displacement reactions Decomposition reactions
Displacement E Displacement reactions When one element takes the place of another in a compound. All displacement reactions follow the same format: A + BC AC + B + + B C A C
Displacement reactions E Example If magnesium is added to copper sulfate, magnesium and copper swap places to make magnesium sulfate and copper. Mg MgSO4 Cu CuSO4
I do We do E C When magnesium is added to copper sulfate, magnesium displaces copper to make magnesium sulfate and copper. When zinc is added to lead sulfate, zinc displaces lead to make zinc sulfate and lead. Write the word equation for this reaction. Write the word equation for this reaction. magnesium+ copper magnesium sulfate +copper zinc + lead zinc sulfate + lead sulfate sulfate
I do We do E C When magnesium (Mg) is added to copper sulfate (CuSO4), magnesium displaces copper to make magnesium sulfate (MgSO4) and copper (Cu). When zinc (Zn) is added to lead sulfate (PbSO4), zinc displaces lead to make zinc sulfate (ZnSO4) and lead (Pb). Write the symbol equation for this reaction. Write the symbol equation for this reaction. Zn + PbSO4 ZnSO4+ Pb Mg + CuSO4 MgSO4+ Cu
C If sodium (Na) is added to silver chloride (AgCl), a displacement reaction occurs. What are the reactants? AgCl + Na A NaCl + Ag B NaAg + Cl C
C If sodium (Na) is added to silver chloride (AgCl), a displacement reaction occurs. What are the products? AgCl + Na A NaCl + Ag B NaAg + Cl C
C How can you tell if an equation is displacement? The two reactants are added together to form one product. A There are always two reactants and two products. B Two elements in the reactants will have swapped places in the products. C
Task 3 Displacement reactions P a) Complete the word equations for these displacement reactions. i) calcium ___________ + lithium lithium chloride + calcium ii) sodium chloride + fluorine sodium fluoride + _________ iii) iron oxide + aluminium aluminium _________ + iron iii) silver ________ + copper copper nitrate + silver
Task 3 Answers P a) Complete the word equations for these displacement reactions. chloride i) calcium ___________ + lithium lithium chloride + chlorine calcium oxide ii) sodium chloride + fluorine sodium fluoride + _________ nitrate iii) iron oxide + aluminium aluminium _________ + iron iii) silver ________ + copper copper nitrate + silver
Task 3 Displacement reactions P b) displaces lead to make zinc nitrate Zn(NO3)2and copper Cu. When zinc Zn is added to copper nitrate Cu(NO3)2, zinc i) Write the word equation for this reaction. ii) reaction. Complete the symbol equation for this Zn + Cu(NO3)2
Task 3 Answers P b) zinc displaces lead to make zinc nitrate Zn(NO3)2and copper Cu. When zinc Zn is added to Copper nitrate Cu(NO3)2, i) zinc + copper nitrate zinc nitrate + copper Write the word equation for this reaction. ii) reaction. Complete the symbol equation for this Zn(NO3)2+ Cu Zn + Cu(NO3)2
Lesson outline Chemical reactions Physical and chemical changes Equations Displacement reactions Decomposition reactions
Decomposition reactions E Decomposition reactions When a substance breaks down into two or more smaller components. All decomposition reactions follow the same format: AB A + B + B A
